For the control of their orbit and of their attitude, satellites use an assembly of actuators and, in particular, a set of thrust nozzles.
The thrust nozzle system may comprise thrusters using electrical propulsion or thrusters using chemical propulsion.
In known embodiments, the satellite comprises a hybrid thrust nozzle system, including both thrusters using electrical propulsion and thrusters using chemical propulsion. These thrust nozzles are used separately for maintaining in station of a satellite. In particular, the thrust nozzles using electrical propulsion are used for the control out of the plane of the orbit (generally referred to as “North-South control”), whereas the thrust nozzles using chemical propulsion are used for the control in the plane of the orbit (referred to as “East-West control”), and for the manoeuvres for control of the angular momentum vector (unsaturation or unloading of the flywheels). Such a hybrid system has however a ratio launch-loaded satellite mass over useful mass for the payload and/or the operational lifetime of the satellite which is unfavourable.
In the new generation satellites, “all electric” solutions for all of the elements of the satellite are increasingly being adopted. This “all electric” approach may enable sufficient mass to be gained such that the same launch vehicle can carry two satellites, which results in lower costs for the launch of satellites. Systems of thrust nozzles only comprising thrusters using electrical propulsion have thus been provided. Electrical thrusters offer a better specific impulse than the thrusters using chemical propulsion. However, these “all electric” thrust nozzle systems require additional mechanisms to be provided in the satellite for orientation of the thrust with a narrow angular travel (for example, of the 2-axis thruster orientation mechanism type) or else thrust orientation mechanisms with a wide angular travel (for example, of the 2-axis, 3-axis or more articulated arm type). However, these mechanisms with a wide travel may exhibit an increased adjustment complexity leading to defects in parallelism and/or in orthogonality and pose problems of reliability. This results in a very degraded operation in the case of a functional loss of an orientation mechanism. Furthermore, they increase the total mass of the satellite, the complexity of the flight software, and also the cost of the onboard equipment.